Method and means for producing oxide of zinc



1-. THOMSON.

METHOD AND MEANS FOR PRODUCING OXIDE 0F ZINC.

APPLICATION HLl lD MAR. 16, I921.

Patented Aug. 15, 1922.

INVENTOR.

UNITED STATES PATENT 'OFFIC JOHN THOMSON, OF BROOKLYN, NEW YORK.

Application filed March 16, 1921.

Toall'whomz't may concern. I

Be it known that-I, JoHN'THoM'soN, a citizen of the United States, and a resident of the borough of Brooklyn, city and State of New York, have invented a Method and Means for Producing Oxide of Zinc, of which the following is a specification.

The method and means of this invention while broadly related to the metallurgy of zinc, particularly pertains to the production of oxide-of-zinc, that is when derived from the re-distillation of. metallic zinc; which, in its gaseous form, is then completely oxidized, according to the formula ZI1+O=ZI10.

In that the following data, although academic, are pertinent to the subject matter hereof, it seems pertinent to briefly recite them, as by way of a prefatorial illucidation:

Thus, the re-distillation of impure zinc serves to purify it. For example, a low-- grade metal, whose content of zinc may not exceed 95 to 97 per centum, can be so refined as to yield, by analysis, but a few hundredths of one per centum of deleterious substances.

hen zinc-oreis reduced, as by carbon, in a fuel-fired furnace, and the fume developed therefrom is burned to ZnO, a large additional volume of a residuum, which is principally composed of the products of combustion. mixed with the zinc-fume. Atmospheric air is also introduced, both for the purpose of oxidizing the volatilized zinc and to consume particles of floating. carbon.

When zinc-fume is produced by re-distillationand is thenburned to ZnO' by commingling it with air alone, there is'a large excess volume of gas, chiefly nitrogen, whose volume has been considerably increased by heat derived from the reaction. Moreover the volume of air necessary to introduce is much in excess of what would be theoretically oxygen to effect the transmutation of the fume into ZnO. Consequently, these residuum gases, which must'be evacuated from the oxidizing chambers, act as conveyors of the fluffy oxide. philosophers wool);

hence the necessity for capacious flues, settling chambers, bags, blankets, or screens, whereby to entrain the floating particles but Specification of Letters Patent.

mustJoe evacuated, would normal gas has to be dealt with, as

required tofurnish sufiicient METHOD AND MEANS FOR PRODUCING OXIDE 0F ZINC.

PatentedAug. 15 1922. Serial No. 452,641.

to permit the gases to escape through the meshes.

Again, when zinc is re-distilled in retorts or crucibles, the heat being transferred to the charge through the walls of the refractory containers, the developed fume rising from the relatively restricted area of the face of the charge, thence directly fiowin intoa chamber to be burned to ZnO, the temperature of said fume can be but little above that of the boiling point of the zinc; which is ordinarily taken at about 925 C. A cubic foot of oxygen, at-atmospheric pressure, may be taken as weighing .089 pound; and one pound of zinc-fume, at or about its temperature of evolution, hasan approximate volume, according to various authorities, of 5.5 cubic feet.

ure oxide-of-zinc has the approximate relative composition of 80.34 parts zinc and at atmospheric pressure, approximating 4,500 cubic feet.

If the foregoing volume of oxygen were derived from air, the inert nitrogen, which wards of 18,000 cubic feet, that-is depending upon the extent of its expansion by heat; which is derived both from the reaction and subsequent contact with the hot ZnO.

t is now commercially feasible to electrolytically generate practically pure oxygen, at such a relatively moderate cost that its utilization is not only commercially feasible for the production of ZnO from re-distilled ly be upzinc, but various substantial advantages are derived by the utilization of the method and means of the present invention; the essence of which will now be briefly summated, namely: .0

To produce, in an electric furnace, by redistillation of"metallic zinc, substantially pure, isolated zinc-fume, or zinc-gas; to super-heat the said fume'wit'hin the said furnace; to pass the said super-heated fume into a separate, contiguous chamber; and to supply said chamber either with pure or partially depotentiated generated oxygen, whereby to efi'ect the reaction (Zn|-O:Zn()) either without a gaseous residuum, or a substantially lesser gaseous residuum than would be produced if atmos-' pheric air were used as the sole oxidizing agent, whereby there will be practicall 1 no impedance to the descent of the Zn to the bottom of the precipitating chamber, Whose volumetric capacity may be very much less than would otherwise be necessary.

At the present time, the largest employment of ZnO is for the vulcanization of rub ber, particularly automobile tires, and for this purpose the more complete and uniform is the state of its'comminution the more effective is the result, whence the tradeslogan: The finer it is, the better it is.

The next largest employment of ZnO is for pigments; and, in this field, apart from the necessity of being one-hundred per centum white (which is largely a function of the purity of the zinc-gas) the matter of fineness is also highly important, in that the finer it is, the denser, as a paint, will be the film and the greater will be the area of its covering capacity.

In the drawings, which constitute a part of this specificationbut have been more particularly prepared to visualize preferred means for the realization of this method,

Figure 1 is a plan view of an electric furnace and a co-ordinating precipitating chamber, whose covers are removed, taken along the planes A and B of Figure 2.

' Figure 2 is a vertical, longitudinal section, as along the center line C, C of Figure 1;

Figure 3 is a vertical transverse section through the main portion of the precipitating chamber, as along the line D, D of Figure 1; and

Figure 4 is a detached, enlarged, transverse sectional diagram of the tubes L, M, as disposed in Figure 2.

The furnace element here denoted, E, is preferably of the resistance type in which heat is developed by a zigzag carbon resistor F, suspended above a tank H, which contains the molten zinc 4:. The said resistor is preferably so formed, as is indicated in Figure 2, that its lower surface has a higher current-density and a correspondingly higher temperature, than its upper surface. Its terminals 5,6, are connected in g ppwer circuit, as is symbolically denoted When the zinc is generated as a gaseous fume, at the surface of the bath, it flows upwardly, primarily impinging upon and passing around the hotter surfaces of the resistor, as see arrows a,'b, 0, and is thereby superheated and expanded. a

In connection with the foregoing, it is pertinent to here inject that, as seems to have been indubitably proven by competent investigators, zinc-fume, or, as it is also quently, the object of super-heating the generated zinc-gas, as an element of this method, is to deliver it into the oxidizing chamber in the finest state of atomic comminution which is physically possible to attain; and to also adequately supercharge it with heat units, whereby to absolutely prevent a transposal to the mist-stage prior to its complete oxidization.

Continuing the elemental description of the means for realizing this method: the super-heated zinc-gas passes out of the fuming furnace, as see arrow d, through ports J, J J into the interior of the precipitator, K. Said ports are preferably narrow in vertical section, virtually forming slits along the length of the precipitating chamber, whereby to deliver a relatively thin ribbonlike stream of zinc-gas.

Contiguous to the outlets of said ports are two horizontal, parallel tubes, one of which, L, is disposed above the ports, whilst the other, M, is beneath them. These tubes are rovided with slits, as 7, 8, or numerous per orations, so located that the out-flow therefrom shall tend to converge one towards the'other, as see arrows e, it. These tubes are for the purpose of supplying, as

from a source, or sources, of supply N, N either generated oxygen alone; or a combination therewith of atmospheric air; or one tilbe, preferably the upper, may supply pure undepotentiated oxygen, and the other tube may supply atmospheric air alone, or depotentiated oxygen, as the case and need ma be.

hus, it will be perceived that the outflowing volume of super-heated zinc-gas is completely blanketed, above and below, with impinging streams either of pure oxygen,

' or one of oxygen and one of air, or a stream or streamsof depotentiated oxygen, resulting in a very rapid and complete transmus tation of the zinc-gas and oxygen to Zn(). In fact, the reaction may be largely if not wholly completed within ashort distance from the zone of primary impingement.

The interiorof the precipitator may. be divided into sub-chambers, P, P P as by division walls R, R leaving end-openings,

whereby there will be a sinuous, horizontal mentally afiected fuse, or partially tion of temperature lIL the oxide.

flow therethrough, as see arrows 2', m, the volumetric extent of which will depend upon the residuum of gas, or gases. At the far end of the chamber is a vent-pipe T.

In normal practice, the volumetric precipitation, of the oxide V, progressivelydecreases, as see arrows r, s, t, Figure 2, from the forward tothe rearward portion of the chamber. Extraction of the oxide may be made through a side opening, as Y.

The actual utilization of pure oxygen has been found to be greater than was primarily deemed likely, some 85 percentum of the volume supplied having been attained, whilst an ultimate efficiency of fully 90 per centum appears to be a justifiable expectancy.

When pure oxygen alone is employed, and with so high a utilization thereof as has just been cited, the excess volume is relatively so limited, and its velocity of flow so slow, that, as has been picturesquely expressed, the oxide falls like snow in a motionless atmosphere. In fact, the precipitation may then be so concentrated in area that it requires too frequent extractions from the floor of the primary portion of the chamber. Thus, it has been demonstrated, as had been theoretically presumed, that a certain addition of atmospheric air may be advantageously employed, for example as follows: F irstly, through its content of nitrogen, to serve as a conveyer of the oxide, whereby to effect a greater area of its distribution; secondly, to

diminish the quantity of generated oxygen by the amount that air-oxygen may be utilize; and, thirdly, to serve as an absorbent of heat. No difficulty has been encountered in practice, respecting which there was some theoretical apprehension, from anexcessive development of heat, engendered by the exothermic reaction, which would have detrithe product, such as to fuse, clinker or sinter the oxide.- Therefore, the quantity of atmospheric air which may be advantageously employed appears to be adequately determinable merely by consideration of two factors, namely (a) the cubical capacity of the precipitating chamber (the more air the larger the chamber) and (b) the extent of diminu- For it should here be borne in mind that the heat imparted to any oxygen in excess of that required for oxidization, and to any relatively large volume of nitrogen, must be wholly derived from the super-heat imparted to the zinc-gas plus that developed by the reaction. Consequently, as it has been shown that oxide of the highest state of fineness can only be derived by completely oxidizing the zincgas when it is a gas, in contradistinction to its condition as a mist, it seems'probablealthough this is 'not submitted as a definite limit that the maximum amount of airoxygen which may be effectively employed, in the practice of this process, ranges in the neighborhood of, say, 15 to 20 percentum of the total oxygen required to produce a given quantity of ZnO.

If, or when, air is employed, it may be mixed with the generated oxygen, whereby the latter would be depotentiated, or it may be separately introduced through one or the pipe.

Suction may be applied to the vent-piper;

a bag may also be attached thereto, whereby the utmost extent of distribution of the oxide within the precipitator would ensue, plus some minor portion gathered in said bag.

Whilst it is true that the cost of electrolytically generated oxygen may be greater, per se, than that derivable from free air, yet the allied advantages notvonly balance but distinctly exceed the difference in this item of the cost, as a whole, of the produced oxide. For example, instead of deriving a product comprised in different grades, commanding from the lowest to the highest market prices, there is, by this method, practically but one grade; that is a grade which is higher than that of the highest established commercial standards; and, moreover, it is susceptible of being sold at, or even higher than that of, the highest price of the highest grade otherwise produced. The cost of equipment, plant, ground and attendance is relatively nominal compared to that of prior practice; The up-keep cost of the furnace,

precipitator and oxygen generator is practically a negligible factor. established wherever power, zinc, shipping facilties and purchasers are most desirably grouped. Again, when the electrolytic oxygen plant is locatg@as in many instances it can bewhere the derived hydrogen can be disposed of at its establishedvalue, the oxygen becomes a by-product and its cost would then be equalto that of free air; but with a commercial potentiality, technically and commercially, far (in excess of the latter.

Themeans which'have been cited for realizing the present method may-be variously modified without evasion of the spirit and functioning thereof; for example, in support of this assertion andto justify several of the following generic claims, a plurality of precipitating chambers may be connected to the fuming furnace; the oxygen, or oxygen and Plants may be air, need not necessarily be introduced along a single zone of the precipitating chamber but may be injected at different portions thereof; so, too, the zinc-gas, or the oxygen, orthe air, or any of them separately or variously combined, may be extraneously superheated, as within an intermediary chamber or in the precipitator itself, whereby the essence of this method would be attained although the simpler means and disposals herein depicted and described are manifestly preferable.

WVhat I claim is:

1. The method of producing oxide-of-zinc which consists in oxidizing relatively pure, isolated zinc-gas by means of generated oxygen, said zinc-gas being formed by the redistillation of metallic zinc.

2. The method of producing oxide-ofzinc which is comprised in commingling generated oxygen with zinc-gas formed by redistillation.

3. The method of producing oxide-of-zinc which consists in commingling generated oxygen with isolated zinc-gas formed by redistillation, the oxygen being supplied in a volume somewhat in excess of that theoretically required to effect complete oxidization of the zinc-gas.

4. The method of producing oxide-of-zinc which is comprised in commingling isolated zinc-gas, formed by re-distillation, with generated oxygen whose potency has been reduced by an admixture of atmospheric air.

5. The method of producing oxide-of-zinc which is comprised in commingling isolated zinc-gas, formed by re-distillation, with a mixture of generated oxygen and atmospheric air whose relative proportions are such that the gaseous residuuin is substantially less than if air alone were used.

a 6. The method of producing oxide-of-zinc essentially consisting in oxidizing relatively pure, isolated zinc-gas by partially depotentiated generated oxygen, the zinc-gas being produced by re-distillation of metallic zinc in an electric furnace from whence it passes between impinging streams of the oxidizing medium, the oxide concurrently precipitating in a chamber.

7 The method of producing oxide-of-zinc' essentially consisting in oxidizing relatively pure, isolated zinc-gas by depotentiated generated oxygen, the zinc-gas being produced by re-distilling metallic zinc in an electric "furnace from whence it passes through a V port or portsacross an implnglng stream, or

streams, of the oxidizing medium supplied by a perforatedor slitted pipe, or pipes,

the oxide concurrently precipitating in a chamber.

8. The method of producing oxide-of-zinc essentially consisting in oxidizing relatively pure, isolated zinc-gas by means of depotentiated generated oxygen, the fume being produced by re-distillation and caused to How through or above or beneath an impinging stream, or streams, of oxygen, a portion of the oxide immediately precipitating whilst the remainder floats between, and thence around the ends of, battle walls, in a sinuous horizontal plane, concurrently precipitating upon the floor of the chamber.

9. The method of producing oxide-of-zinc which is comprised in oxidizing relatively pure, isolated zinc-gas by means of depotentiated oxygen, said zinc-gas being formed, in an electric furnace, by the re-distillation of metallic zinc and then after super-heated prior to its union and reaction with said oxygen.

10. The method of producing oxide-ofzinc which is comprised in commingling depotenti-ated oxygen with re-distilled zinc-gas,

formed in an electric furnace,which is superheated prior to its union and reaction with said oxygen.

11. The method of producing oxide-ofzinc consisting in re-distilling metallic zinc,

in an electric furnace, super-heating the zinc-gas, passing said gas to a separate contiguous chamber wherein it is commlngled with depotentiated oxygen; the product of ling therewith depotentiated oxygen,the ensuing reaction taking place at a temperature which is above that of the mist-phase of zinc-gas.

13. The method of producing oxide-ofzinc which consists in super-heating re-distilled zinc-gas, in an electric furnace whose heat is derived from a ziz-zag carbon resistor, oxidizing the said gas with depotentiated oxygen at a temperature above that of the mist-phase of zinc-gas, and concurrently precipitating the resulting prodnot within the reaction-chamber.

14. The method and means for producing oxide-of-zinc' which are comprised inre distilling zinc and super-heating the evolved gas in an electric furnace having a zig-zag resistor suspended above the fluid bath; passing the gas to a separate, contiguous chamber which is supplied with depotenti-ated oxygen; oxidizing said gas at a temperature above that of its mist-phase and concurrently precipitating theproduced ox- 'ide within the said chamber. 

